Water-Based Wetness-Indicating Composition and Sensor

ABSTRACT

A color-appearing ink composition includes a surfactant blend of at least two non-ionic surfactants having hydrophilic-lipophilic balance values greater than 10, or a non-ionic surfactant having a hydrophilic-lipophilic balance value greater than 10 and a charged surfactant. The composition includes one or more water-insoluble leuco dyes, a developer and a desensitizer. The composition may be applied to a substrate to form a sensor.

This application claims priority to Provisional Patent Application No.61/604,872, filed on Feb. 29, 2012. The entirety of Provisional PatentApplication No. 61/604,872 is incorporated herein by reference.

FIELD OF INVENTION

The present invention pertains to a wetness-indicating composition foran aqueous medium. In particular, the present invention describes awater-based medium or ink that can change from being colorless tocolored in the presence of an aqueous solution. The ink may be appliedto an article such as a substrate to form a sensor.

BACKGROUND

Many products, including consumer, health care, and professionalproducts, are more effectively used by consumers when containing afeature that can communicate or signal to the user that the product iswetted with an aqueous solution (e.g. urine). One example is a visualwetness indicator that causes the product to change color or appearancewhen wet. Color indicators can either indicate wetness through a changefrom colorless to colored or vice versa, or through a change in colorsaturation.

Exemplary consumer products that could be more effective and delivermore benefits to end users by incorporating a suitable color indicatorinclude absorbent articles such as diapers, feminine pads orincontinence pads and garments. Exemplary professional products thatcould be more effective and deliver more benefits to end users byincorporating a suitable wetness indicator include products for medicaluse such as bed pads or bandages. Other products that can benefit from awater-based color indicator include wipes, towels and tissues.

Wetness-indicating inks for such products are well known. Desirableperformance attributes include durability and non-leachable. These inks,while wettable, are water insoluble.

To date, water-insoluble indicator inks are volatile organicsolvent-based inks that contain water-insoluble dye components (e.g.actives). However, the use of volatile organic solvents not only hindersthe manufacture of the absorbent articles noted above due toincompatibility with the manufacturing process of cellulose-basedproducts, such use is also not environmentally friendly and more costly.

While the color-changing compositions known in the art prevent leachingin aqueous environments, there remains a need for a water-basedwetness-indicating ink that is environmentally friendly and does notleach. Further sought is an ink that is printable at room temperatureand provides a readily discernible color change to the un-aided eye.Desirably, the ink is applicable to various articles includingsubstrates used to make the absorbent articles mentioned herein.

SUMMARY OF THE INVENTION

Disclosed is a water-based wetness-indicating ink that includes leucodyes that are colorless in the presence of a desensitizer. The ink maybe printed and dried onto various articles or substrates used to makevarious articles. When the dried ink contacts water, the desensitizer isdissolved, allowing the leuco dye to interact with a developer toproduce a color.

In one aspect of the disclosure is a method for preparing a substrate,the method having the steps of preparing a surfactant blend comprisingat least two surfactants having different hydrophilic lipophilic balanceprofiles; preparing a solubilized active by solubilizing awater-insoluble leuco dye with the surfactant blend and a developer;combining the solubilized active with a binder, a stabilizer and waterto create a colored solution; applying the colored solution to thesubstrate; and drying the substrate so that the applied colored solutionbecomes colorless.

In another aspect of the disclosure is a color-appearing ink compositionincluding a surfactant blend having at least two non-ionic surfactantshaving hydrophilic-lipophilic balance values greater than 10. Thecomposition further includes a water-insoluble leuco dye, a developer, adesensitizer, a binder, a stabilizer, and water. In a further aspect,the composition may be applied to a substrate to create a sensor.

In another aspect of the disclosure is a color-appearing ink compositionhaving a surfactant blend including a non-ionic surfactant having ahydrophilic-lipophilic balance value greater than 10, and a chargedsurfactant. The surfactant may be anionic, amphoteric or zwitterionic.Further included is a water-insoluble leuco dye, a developer, adesensitizer, a binder, a stabilizer, and water. In a further aspect,the composition may be applied to a substrate to create a sensor.

Additional features and advantages of the water-based wetness-indicatingink will be described in the following detailed description. It isunderstood that the foregoing general description and the followingdetailed description and examples are merely representative of theinvention, and are intended to provide an overview for understanding theinvention as claimed.

BRIEF DESCRIPTION OF FIGURES

FIG. 1. Shown is a schematic of how the water-based functional ink ofthe present invention develops color in the presence of water.

FIG. 2. Shown is polyethylene film treated with several solutions of thepresent invention, the solutions containing betaine (75 wt. %) 4,4-DHBP(left), 2,4-DHBP (left middle), 2,2′4,4′-DHBP (right middle), and 2,2′DHBP (right), wherein the intensity of each sample was monitored afterbeing wetted with water for 0, 30, 120, and 300 seconds.

FIG. 3. Shown are seven commercial water-based binders with Green-2 dyeat 20, 40 and 60 wt. % binder for each.

FIG. 4. Shown are four leuco dyes, Green-2, CVL, Red-40 and 1:4CVL/Red-40 blend, combined with 40 wt. % AQUAKING varnish.

FIG. 5. Shown is the effect of sonication on stability of thewetness-indicating ink of the present invention.

DETAILED DESCRIPTION

The present invention relates in part to a water-basedwetness-indicating ink composition that includes multiple components.The ink is effective even when employing only a single dye. The ink maybe applied to a substrate or other object by means of conventionalprinting techniques. Other application techniques include spraying,painting or dipping. In one aspect, the ink includes a color-developingcomposition that can change from a largely colorless or pale appearanceto a visually distinct or vibrant color when the film layer is exposedto a change in its immediate physical or chemical environment as aresult of the introduction of an aqueous medium or mixture.

Referring to FIG. 1, the water-based indicating ink includes leuco dyesthat are colorless in the presence of a desensitizer. When the ink, in adry state, contacts water, the desensitizer dissolves allowing the leucodye to interact with a developer. This interaction produces a color.

Mixtures of at least two surfactants with varying hydrophilic-lipophilicbalance values are used to solubilize the active water-insoluble dyecomponents. This is the basis of the ink and is referred to as thecolor-developing composition. Other water-soluble additives may becombined with the color-developing composition to create the inkformulation of the present invention. These additives include an inkbinder, a desensitizer, a developer, an ink stabilizer and free water.

Section I

Color-Developing Composition

The present invention involves a color-developing composition thatcontains at least three major components: (1) a leuco dye, (2) adeveloper and (3) two surfactants each having a differenthydrophilic-lipophilic balance. In addition to these main threecomponents, the color-developing composition may also contain otheradditives to adjust the physical properties thereof.

Leuco dyes are generally referred to as colorless or pale-colored basicdyes, because the dye molecules can acquire two forms, one of which iscolorless. Although not intended to be bound by theory, it is believedthat the color developer agent functions as a Lewis acid, whichwithdraws electrons from the leuco dye molecule to generate a conjugatedsystem. Hence, the leuco dye appears to manifest color from anoriginally colorless state.

The leuco dyes that may be employed can be selected from a variety ofdyes including, for example, phthalide leuco dyes, triarylmethane leucodyes, and fluoran leuco dyes. Specific examples include (1)Triarylmethane-based dyes, e.g.3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide,3,3-bis(p-dimethylaminophenyl)phthalide,3-(p-dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl)phthalide,3-(p-dimethylaminophenyl)-3-(2-methylindol-3-yl)phthalide,3,3-bis(1,2-dimethylindol-3-yl)-5-dimethylaminophthalide,3,3-bis(1,2-dimethylindol-3-yl)-6-dimethylaminophthalide,3,3-bis(9-ethylcarbazol-3-yl)-6-dimethylaminophthalide,3,3-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide,3-p-dimethylaminophenyl-3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide,etc. (2) Diphenylmethane-based dyes, e.g.,4,4′-bisdimethylaminobenzhydryl benzyl ether, N-halophenylleucoauramine,N-2, 4,5-trichlorophenyl-leucoauramine, etc. (3) Lactam-based dyes,e.g., rhodamine-B-anilinolactam, rhodamine-(p-nitroanilino)lactam,rhodamine-(o-chloroanilino)lactam, etc.

(4) Fluoran-based dyes, e.g., 3-dimethylamino-7-methoxyfluoran,3-diethylamino-6-methoxyfluoran, 3-di-ethylamino-7-methoxyfluoran,3-diethylamino-7-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran,3-di-ethylamino-6,7-dimethylfluoran,3-(N-ethyl-p-toluidino)-7-methylfluoran,3-diethylamino-7-(N-acetyl-N-methylamino)fluoran, fluoran,3-diethylamino-7-(N-methylamino)fluoran,3-diethylamino-7-dibenzylaminofluoran,3-diethylamino-7-(N-methyl-N-benzylamino)fluoran,3-diethylamino-7-(N-chloroethyl-N-methylamino)fluoran,3-diethylamino-7-N-diethylaminofluoran,3-(N-ethyl-p-toluidino)-6-methyl-7-phenylaminofluoran,3-(N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino) fluoran,3-diethylamino-6-methyl-7-phenylaminofluoran,3-dibutylamino-6-methyl-7-phenylaminofluoran,3-diethylamino-7-(2-carbomethoxyphenylamino) fluoran,3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluoran,3-pyrrolidino-6-methyl-7-phenylaminofluoran,3-piperidino-6-methyl-7-phenylaminofluoran,3-diethylamino-6-methyl-7-(2,4-dimethylamino)fluoran,3-diethylamino-7-(o-chlorophenylamino)fluoran,3-dibutylamino-7-(o-chlorophenylamino)fluoran,3-pyrrolidino-6-methyl-7-(p-butylphenylamino) fluoran,3-(N-methyl-N-n-amylamino)-6-methyl-7-phenylaminofluoran,3-(N-ethyl-N-n-amylamino)-6-methyl-7-phenylaminofluoran,3-(N-ethyl-N-isoamylamino)-6-methyl-7-phenylaminofuluoran,3-(N-methyl-N-n-hexylamino)-6-methyl-7-phenylaminofluoran,3-(N-ethyl-N-n-hexylamino)-6-methyl-7-phenylaminofluoran,3-(N-ethyl-N-β-ethylhexylamino)-6-methyl-7-phenylaminofluoran, etc. Thebasic dyes useful in this invention are not limited to those exemplifiedabove.

Suitable surfactants for usage in this invention include charged anduncharged surfactants. The hydrophobic/lipophilic balance (“HLB”) valueof the surfactant is a factor in the selection of an unchargedsurfactant. An HLB less than 10 indicates more hydrophobic properties,and an HLB value greater than 10 indicates more hydrophilic properties.With lower HLB values (i.e. less miscible with water), surfactants arenot able to fully dissolve the leuco dyes. As the HLB value increase,the surfactants become more effective at dissolving the leuco dye.

Table 1 provides a non-exhaustive list of various surfactants that maybe suitable for the present invention. The listed surfactants aresuitable for dissolving formulation components such as the leuco dye.

TABLE 1 Surfactants Surfactant HLB Trade Name INCI Name value VendorLUMULSE 40-L PEG-8 Laurate 12.8 Lambent Technologies TRITON X-100Octoxynol-9 13.5 Dow Chemical Company TWEEN 80 Polysorbate 80 18.0Sigma-Aldrich DOWFAX 2A1 Disodium Lauryl Phenyl Ether >20.0 Dow ChemicalDisulfonate Company

For uncharged surfactants, nonionic surfactants with HLB greater than 10are advantageous. Non-limiting examples of nonionic surfactants with anHLB greater than 10 are PEG-8 Laurate, Octoxynol-9 and Polysorbate-80.

Charged surfactants include anionic, amphoteric, and zwitterionicsurfactants. Charged surfactants do not fit the requirements tocalculate an HLB value. Based on performance, they show a solubilizationcapability exceeding an HLB value of 20. Specific examples of suitablecharged surfactants include but are not limited to Disodium LaurylPhenyl Ether Disulfonate.

Suitable developers generally include bisphenol A, zinc chloride, zincsalicylate, gallate derivatives such as octyl gallate, propyl gallate,and lauryl gallate, and phenol resins. The most desirable gallatedeveloper is octyl gallate due to its ability to yield a quick, vibrantcolored response upon insult.

Suitable developers further include 2,4-dihydroxybenzophenone;4,4′-dihydroxybenzophenone; 2,2′,4,4′-dihydroxybenzophenone; and2,2′-dihydroxybenzophenone. Of these developers, the4,4′-dihydroxybenzophenone (“4,4′-DHBP”) is most desirable due to avibrant color response and absence of yellowing of the substrate towhich it may be applied. See FIG. 2.

Other examples of developers that may be used conjointly with the lecuodyes may include: 4-tert-butylphenol, a-naphthol, β-naphthol,4-acetylphenol, 4-tert-octylphenol, 4,4′-sec-butylidenephenol,4-phenylphenol, 4,4′-dihydroxydiphenylmethane, 4,4′-isopropylidenediphenol, hydroquinone, 4,4′-cyclohexylidene diphenol, 4,4-dihydroxydiphenylsulfide, 4,4′-thiobis(6-tert-butyl-3-methylphenol),4,4′-dihydroxydiphenyl sulfone, hydroquinone monobenzyl ether,4-hydroxybenzophenone, 2,4,4′-trihydroxybenzophenone,2,2′,4,4′-tetrahydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate,sec-butyl 4-hydroxybenzoate, pentyl 4-hydroxybenzoate, phenyl4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate,chlorophenyl 4-hydroxybenzoate, phenylpropyl 4-hydroxybenzoate,phenethyl 4-hydroxybenzoate, p-chlorobenzyl 4-hydroxybenzoate,p-methoxybenzyl 4-hydroxybenzoate, novolak type phenol resins, phenolpolymers and like phenol compounds.

Section II.

Wetness-Indicating Ink

To prepare a color-appearing wetness-indicating ink, thecolor-developing composition of the present invention is added to asolution containing a desensitizer, a binder, a stabilizer and freewater.

Suitable desensitizers are water soluble, of low molecular weight andpreferably zwitterionic. Examples of such desensitizers include betaine(trimethylglycine), sodium bis-hydroxyethylglycinate lauryl-glucosidescrosspolymer, sodium bis-hydroxyethylglycinate coco-glucosidescrosspolymer (available from Colonial Chemical, Inc.), betaineester-menthol and betaine hydrochloride. Other zwitterionic moleculesinclude 2-(methacryloyloxy)ethyl 3-sulfopropyl ammonium hydroxide andother related ammonium hydroxide derivatives.

Among these desensitizers, betaine derivatives having an averagemolecular weight of about 100 to about 800 are desirable because the useof such a desensitizer results in excellent decolorization and colorformation without tackiness.

The desensitizer is used in an amount effective to inhibit the colorforming reaction between the basic dye and the color developing materialin the absence of water in the water-sensitive coloring layer. Theamount is influenced by factors such as formulation components andamounts thereof, the concentration of the coating composition forforming the water-sensitive coloring layer, the substrate porosity, etc.

Suitable binders are water-based emulsions of water-insoluble polymersbinders, cellulose derivatives, polyamides and their copolymers,polyesters and their copolymers, phenolic resins and polyanhydrides. Onedesirable and commercially available water-soluble binder is AQUAKINGVehicle TV94-5865 (available from Sun Chemical Company).

Stabilizers prevent precipitation of dye components or layer separationwithin the ink composition. One desirable stabilizer ishydroxypropyl-modified guar gum. Other suitable stabilizers include gumarabic, guar gum, xanthan gum, hydroxyethyl cellulose, methyl cellulose,ethyl cellulose, starches, casein, gelatin, and water-soluble polymerssuch as polyvinyl alcohol and styrene-maleic anhydride copolymer salt.

The leuco dyes can be present in the composition from about 0.01 wt. %to about 10 wt. %. Typically the amount of leuco dye can be betweenabout 0.05 or 0.1 wt. % to about 4 or 5 wt. %, or 6 or 7 wt. %;desirably the range is between about 0.5 or 1 wt. % to about 2.5, 3 or 5wt. %, inclusive. The amount of the surfactant blend typically ispresent from about 1 wt. % to about 15 wt. % or 30 wt. %. Alternatively,the surfactants can be present from about 1, 5, 10 wt. % to about 5, 15,or 30 wt. %, inclusive. The amount of desensitizer typically is presentfrom about 1 wt. % to about 15 wt. % or 30 wt. %. Alternatively, thedesensitizer can be present from 1, 10, or 25 wt. % to about 1, 5, or 15wt. %, inclusive. The amount of developer that is present can range from1, 10, or 25 wt. % to about 1, 5, or 15 wt. %; typically, between about1 wt. % to about 25 wt. %. The amount of binder that is present canrange from about 10 wt. % or 25 wt. % to about 30 wt. % or 50 wt. %;typically, between about 20 wt. % to about 40 wt. %. The stabilizer ispresent from about 0.01 wt. % to about 1 wt. %. Typically, the amount ofstabilizer is between about 0.1 wt. % to about 0.5 wt. %, inclusive.Finally, the amount of free water typically is present from about 20 wt.% to about 90 wt. %; typically, between about 25, 30, or 35 wt. % toabout 80, 85, or 88 wt. %, inclusive.

Section III.

Printed Articles

The water-based wetness-indicating ink may be printed or otherwisedisposed on various articles or materials. In an aspect of the inventionwhere the ink functions as a color-appearing ink, the formulation, wheninitially applied to the article, appears colored until air-dried to acolorless or nearly colorless state of appearance (i.e., either no coloror very weak background shade). The dried inks show various colors uponbeing wetted depending on the kind of leuco dye used. Once theindicating ink is printed and dried on the surface of the substrate, thedried solution can manifest color when it contacts a water-containingmedium.

In other aspects, a wetness sensor may be composed of a substrate ontowhich the wetness-indicating ink is deposited. The substrate can be anysubstrate that allows a deposition of the indicator ink composition toexhibit a color. The substrates may be porous or non-porous. Examples ofvarious substrates include, but are not limited to, porous tissues,papers, polymeric films, metals, wood, plastics, rubbers, wovenmaterials and nonwoven materials that may include a calcium carbonatefiller.

“Nonwovens” are materials and webs of material that are formed withoutthe aid of a textile weaving or knitting process. For example, nonwovenmaterials, fabrics or webs have been formed from many processes such as,for example, meltblowing processes, spunbonding processes, air layingprocesses, coform processes, and bonded carded web processes.

“Coform” refers to a blend of meltblown fibers and absorbent fibers suchas cellulosic fibers that can be formed by air forming a meltblownpolymer material while simultaneously blowing air-suspended fibers intothe stream of meltblown fibers. The meltblown fibers and absorbentfibers are collected on a forming surface, such as provided by a belt.Two U.S. patents describing coform materials are U.S. Pat. No. 5,100,324to Anderson et al. and U.S. Pat. No. 5,350,624 to Georger et al., bothof which are incorporated in their entirety in a manner consistentherewith.

“Meltblown” refers to fibers formed by extruding a molten thermoplasticmaterial through a plurality of fine, usually circular, die capillariesas molten threads or filaments into converging high velocity gas (e.g.,air) streams, generally heated, which attenuate the filaments of moltenthermoplastic material to reduce their diameters. Thereafter, themeltblown fibers are carried by the high velocity gas stream and aredeposited on a collecting surface or support to form a web of randomlydispersed meltblown fibers. Such a process is disclosed, for example, inU.S. Pat. No. 3,849,241 to Butin et al. which is incorporated in theirentirety in a manner consistent herewith.

“Spunbonded fibers” refers to small diameter fibers which are formed byextruding molten thermoplastic material as filaments from a plurality offine, usually circular capillaries of a spinneret with the diameter ofthe extruded filaments then being rapidly reduced to fibers as by, forexample, in U.S. Pat. No. 4,340,563 to Appel et al.; U.S. Pat. No.3,692,618 to Dörschner et al.; U.S. Pat. No. 3,802,817 to Matsuki etal.; U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney; U.S. Pat. No.3,502,763 to Hartman; and U.S. Pat. No. 3,542,615 to Dobo et al., thecontents of which are incorporated herein by reference in their entiretyin a manner consistent herewith.

In accordance with the present disclosure, one or more sensors describedherein can ultimately be integrated into an absorbent article. An“absorbent article” generally refers to any article capable of absorbingwater or other fluids. Examples of some absorbent articles include, butare not limited to: personal care absorbent articles, such as diapers,training pants, absorbent underpants, incontinence articles, femininehygiene products (e.g., sanitary napkins), swim wear, baby wipes, and soforth; and medical absorbent articles, such as garments, fenestrationmaterials, under-zones, bed-zones, bandages, absorbent drapes, andmedical wipes, food service wipers, clothing articles, and so forth.Materials and processes suitable for forming such absorbent articles arewell known to those skilled in the art. Many of the above-notedabsorbent articles include a substantially liquid-impermeable layer(e.g., outer cover), a liquid-permeable layer (e.g., bodyside liner,surge layer, etc.), and an absorbent core.

The wetness-indicating ink is applied either at discrete localized spotson the surface of said substrate or generally over the entire substrateor article surface. Alternatively, the indicating ink is applied to samein different patterns and shapes. The substrate or article may havemultiple indicating inks applied to different portions thereof.

Section IV.

EXAMPLES Water Tolerability

To determine the miscibility of the surfactants with water, 1 mL of eachsurfactant of Table 1, (supra) was tested with increasing percentages ofwater ranging from 30-90% total volume. A 1:5 crystal violet lactone:4,4′-DHBP powder blend (0.2 g) with betaine (1 mL of 1 g/mL in water)was added to ensure that the formulation components were compatible withthe water-based wetness-indicating ink. Upon stirring, the solutionswere visually inspected to evaluate such compatibility. PEG-8 Laurateand Polysorbate-80 showed the highest compatibility with components andwater respectively. PEG-8 Laurate and Polysorbate-80 were tested incombination. Weight percent ratios of 1:1, 3:1, 5:1 of PEG-8 Laurate andPolysorbate-80 were tested at the aforementioned volume percentages ofwater. The color response intensity of the inks was reevaluated todetermine optimal ratios of ink components. A small amount of the 1:5crystal violet lactone: 4,4′-DHBP powder blend (0.2 g) was stirred into1 mL of the surfactant mixtures. Once a strong blue color was seen, 1 mLof the betaine solution (1 g/mL in water) and the appropriate amount offree water were added. The resulting ink was disposed onto cellulosicfilter paper and, after drying, appeared colorless. Upon insult withwater, a colored response was observed. The strongest color-appearancewas observed with formulations using 3:1 and 5:1 PEG-8Laurate:Polysorbate-80 mixtures. (The 3:1 mixture is hereinafterreferred to as the “surfactant mixture”).

Addition of Binders:

To determine the binder compatibility with the color-developingcomposition, seven commercial water-based binders were tested withGreen-2 leuco dye. Binders were mixed at 0, 20, 40, and 60 total weightpercent with 1 mL (10 wt. %) of the surfactant mixture and appropriatefree water.

As seen in FIG. 3, some of the binders assisted in color intensityenhancement, while others did not allow any color development at all.The binder which yielded the most vibrant color response (Binder 7:AQUAKING Vehicle TV94-5865; 40 wt. % (“AQUAKING varnish”)) was furtherevaluated with additional leuco dyes as seen in Table 2 (Green-2, CVL,Red-40, and CVL/Red-40 blend) to determine the functionality of eachcolor-developing composition with a selected binder. The dye:developervolume ratios differed for each dye as indicated in Table 3. TheAQUAKING binder was compatible with all tested formulations as seen inFIG. 4.

TABLE 2 Green-2 CVL Red-40 Purple Volume Ratio of 1:6 1:5 1:8 1:6(dye-1:4 Dye:Developer CVL:Red-40) Desensitizer: All contain 600 μL 700μL 1200 μL 800 μL betaine water (4.3 g) and varnish betaine betainebetaine solution (4.0 g) solution solution solution

Stabilizers:

Stabilizers prevent precipitation of formulation components or layerseparation within the formulation. Stabilizers were tested in varyingweight percentages of the total formulation weight. These formulationscontain wetness-indicating ink components: dye (Green-2), developer 11(4,4′-DHBP), desensitizer (betaine), binder (AQUAKING varnish), freewater and the stabilizers below. Guar and xanthan gums were tested at0.20, 0.35, and 0.42 wt. % by making 10.0 mg/mL stock solutions of theindividual gums and adding 2.0, 3.5, and 4.2 mL respectively.Hydroxyethylcellulose (HEC) was tested at 0.35, 0.55, and 0.75 wt. % bymaking 20 mg/mL and 40 mg/mL stock solutions and adding 1.75, 2.75, and3.75 mL respectively. Hydroxypropyl-modified guar gums, JAGUAR HP 8 FF,JAGUAR HP 60, JAGUAR HP 105, and JAGUAR HP 418, were tested at 0.20,0.35, 0.45, 0.50, 0.60, and 0.70 wt. % with 10 mg/mL and 15 mg/mL stocksolutions. Vials of the wetness-indicating ink were allowed to sit for24 hours to monitor settling. While the formulation withhydroxypropyl-modified guar gum JAGUAR HP 60 (0.70 wt. %) exhibited thebest stability and color development upon insult with water, it did notcompletely remedy the layer separation and/or precipitation offormulation components. Other methods of solubilization may be desiredin place of or in addition to the stabilizer.

Micelle Formation with Sonication:

Without being bound by theory, it is thought that ultrasonic bombardmentassists in the formation of small micelles. Therefore, sonicationexperiments were performed to see if solutions may be stabilized with asonification process.

First, four sets of solutions were prepared, three solutions per set.All twelve solutions

1(A, A2 and B, B2), 2(A, A2 and B, B2) and 3(A, A2 and B, B2) consistedof the following: Green-2 dye (30 mg), 4,4′-DHBP (180 mg), 3:1surfactant mixture (1.5 g), water (2.0 g), Jaguar HP 60 stabilizer (4 mLof 15 mg/mL), and Aquaking binder (2.5 g). Solutions 2(A, A2 and B, B2)and 3(A, A2 and B, B2) were the same as solution 1(A, A2 and B, B2) butwith double and triple the amount of surfactant respectively. Further,betaine solution (1.5 mL of 1 g/mL) was added to solutions 1(A2 and B2),2(A2 and B2) and 3(A2 and B2).

Each solution pair was stirred on a hot plate. Solutions 1 B,B2; 2 B,B2;and 3 B,B2; were subjected to one minute of sonication at 20 mHz using aMISONIX™ MICROSON XL sonicating tip.

FIG. 5 shows the results of sonification. In both the first row (withbetaine) and second row (without betaine), it can be seen thatsonication helps to stabilize the solution for a 24 hour period.

Changing Order of Addition of Each Ink Component.

Two solutions were made: one containing dye (30 mg), developer (180 mg),and surfactant (2 g) and the other solution containing water (2.0 g),Hydroxypropyl-modified guar gum (JAGUAR HP 60 (4.0 g)), and binder (2.5g). Each solution was stirred for 3 minutes and vortexed aggressivelyfor 30 seconds, then the surfactant-containing portion was added to thestabilizer-containing mixture and the combined solution wasstirred/vortexed.

Preparing the solution separately in two parts, A and B, and thensubsequently combining the two parts was found to 1) be a more efficientmethod of mixing, and 2) increase the stability of the formulation overa 48-hour period. When this ink was disposed onto filter paper, allowedto dry, and insulted with water, the color response was vibrant.

Water-Indicating Ink Formulation (Weight %):

0.3% Leuco dye (Crystal Violet Lactone)

1.7% developer (4,4′-dihydroxybenzophenone)

6.0% desensitizer (betaine (1 g/mL solution concentration))

10.0% surfactant mixture (3:1 weight % mixture of PEG-8Laurate:Polysorbate-80)

20.0% binder (AQUAKING Vehicle—Sun Chemical)

62.0% water+stabilizer (0.75 weight % JAGUAR HP-60—Rhodia Novecare)

The wetness-indicating ink formulation is prepared from the above-notedcomponents as follows: combine 0.030 g dye and 0.170 g developer with1.0 g surfactant mixture with light heating and heavy stirring topromote complexation. Once a color of relatively high intensity is seen,600 μL of betaine solution is added, which causes the color todisappear. Next, an appropriate amount of water is added to the vialwith constant stirring. An effective amount of stabilizer is then addedand the solution mixed completely. Finally, 2.10 mL of binder is addedto the resulting mixture. The solution is then stirred for about 5minutes.

To prepare test samples, a discrete amount of the mixture is pipettedonto a substrate, and allowed to dry completely. Once dry, a smallamount of water is pipetted onto the dried ink area of the substrate.Upon wetting, a color of relative intensity appears to the unaided eye.

The present invention has been described both generally and in detail byof example. Persons skilled in the art, however, can appreciate that theinvention is not limited necessarily to the embodiments specificallydisclosed, but that substitutions, modifications, and variations may bemade to the present invention and its uses without departing from thespirit and scope of the invention. Therefore, changes should beconstrued as included herein unless the modifications otherwise departfrom the scope of the present invention as defined in the followingclaims.

1. A method for preparing a substrate, the method comprising the stepsof: preparing a surfactant blend comprising at least two surfactantshaving different hydrophilic lipophilic balance profiles; preparing asolubilized active by solubilizing a water-insoluble leuco dye with thesurfactant blend and a developer; combining the solubilized active witha binder, a stabilizer and water to create a colored solution; andapplying the colored solution to the substrate; and drying the substrateso that the applied colored solution becomes colorless.
 2. Acolor-appearing ink composition comprising: a surfactant blendcomprising at least two non-ionic surfactants havinghydrophilic-lipophilic balance values greater than 10; a water-insolubleleuco dye; a developer; a desensitizer; a binder; a stabilizer; andwater.
 3. The color-appearing ink composition of claim 2 wherein thenonionic surfactants are selected from the group consisting of PEG-8Laurate, Octoxynol-9 and Polysorbate-80.
 4. The color-appearing inkcomposition of claim 2 wherein the developer is selected from the groupconsisting of bisphenol A, zinc chloride, zinc salicylate, octylgallate, propyl gallate, lauryl gallate and phenol resin.
 5. Thecolor-appearing ink composition of claim 2 wherein the desensitizer iszwitterionic.
 6. The color-appearing ink composition of claim 2 whereinthe binder is selected from the group consisting of water-basedemulsions of water-insoluble polymers binders, cellulose derivatives,polyamides and their copolymers, polyesters and their copolymers,phenolic resins, and polyanhydrides.
 7. The color-appearing inkcomposition of claim 2 wherein stabilizer is selected from the groupconsisting of hydroxypropyl-modified guar gum, gum arabic, guar gum,xanthan gum, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose,starches, casein, gelatin, polyvinyl alcohol and styrene-maleicanhydride copolymer salt.
 8. A water-based liquid sensor comprising: asubstrate selected from the group consisting of tissue, paper, polymericfilm, woven material and nonwoven material; and a water-soluble inkcomposition disposed on the substrate; the water-based ink compositioncomprising the composition of claim
 2. 9. A color-appearing inkcomposition comprising: a surfactant blend comprising a non-ionicsurfactant having a hydrophilic-lipophilic balance value greater than10, and a charged surfactant selected from a group consisting ofanionic, amphoteric and zwitterionic surfactants; a water-insolubleleuco dye; a developer; a desensitizer; a binder; a stabilizer; andwater.
 10. The color-appearing ink composition of claim 9 wherein thedeveloper is 4,4′-dihydroxybenzophenone.
 11. The color-appearing inkcomposition of claim 9 wherein the desensitizer is a betaine derivativehaving an average molecular weight of 100 to
 800. 12. Thecolor-appearing ink composition of claim 9 wherein the binder isselected from the group consisting of water-based emulsions ofwater-insoluble polymers binders, cellulose derivatives, polyamides andtheir copolymers, polyesters and their copolymers, phenolic resins, andpolyanhydrides.
 13. The color-appearing ink composition of claim 9wherein stabilizer is hydroxypropyl-modified guar gum.
 14. A water-basedliquid sensor comprising: a porous or non-porous substrate; and awater-soluble ink composition disposed on the substrate; the water-basedink composition comprising the composition of claim
 9. 15. The sensor ofclaim 14 comprising a non-woven material.